1. Field of the Invention
The present invention relates to a method and apparatus for managing a plurality of modems in a dial-up network, and more specifically to such a method and apparatus which renders it possible to quickly and economically (in terms of time) determine which one of a plurality of modems has just been installed. The present invention is also applicable to a sub-controller which is provided for controlling a plurality of dial-up modems.
2. Description of the Prior Art
An increasing demand for dial-up (viz., switched) line network services, has required a large number of modems which are concentratedly installed in a networked terminal. It is, accordingly, of considerable importance to effectively manage such a large number of modems and to be able to determine the address at which each unit is located. The modems may be divided into a plurality of groups which are respectively controlled by corresponding sub-control units which are in turn controlled by a main control unit.
As such a dial-up terminal system includes a large number of modems and sub-control units, it is highly desirably to be able to simply and effectively identify the newly installed units via the use of a simple arrangement and method.
Before turning to the instant invention, it is deemed advantageous to discuss a known technique for ascertaining a newly installed modem with reference to FIG. 1. It should be noted that the following discussion relates to the identification of a freshly installed modem.
FIG. 1 shows an arrangement which comprises a main control unit 10, a plurality of sub-control units 12 and 14, and a plurality of modems 10a, 10b, . . . , 10n, 12a, 12b, . . . , 12n, 14a, 14b, . . . , and 14n. Each of the modems 10a-10n, 12a-12n and 14a-14n is provided with a controller which is dedicated to the identification of each unit. Each of these controllers is denoted by the reference numeral of the modem (10a-10n, 12a-12n or 14a-14b) plus a character "c".
As shown, the main control unit 10 is coupled to the sub-control units 12 and 14 via a serial clock line 20a, two serial control lines 20b and 20c. Further, the main control unit 10 is coupled to the modems 10a-10n via a serial clock line 22a, two serial control lines 22b and 22c. On the other hand, the sub-control unit 12 is coupled to the modems 12a-12n via a serial clock line 24a and two serial control lines 24b, 24c. Similarly, the sub-control unit 14 is coupled to the modems 14a-14n via a serial clock line 26a and two serial control lines 26b, 26c.
For the convenience of discussion, it is assumed that: (a) the modem 12b is newly installed and is to be identified by the sub-control unit 12, (b) the maximum number of modems which can be installed under the control of the unit 12 is 255 (=2.sup.8 -1) and (c) each of the modems (installed or not yet installed) is assigned an address (0 to 254 by way of example).
In accordance with a known technique the sub-control unit 12 implements polling at a predetermined time interval by transmitting an address signal via the control line 24b. More specifically, the sub-control unit 12 checks the modems 12a-12n by sequentially changing addresses assigned thereto and receives a response therefrom. The sub-control unit 12 has already identified the already located modems, and hence it can determine the newly installed one (viz., modem 12n) by checking the reply therefrom in response to the polling which has been addressed thereto.
However, the aforesaid known technique has encountered the problem in that the intermittent installation checks, which involves sending-out of all the possible addresses (viz., addresses 0 (for example) to the maximum), is very time-consuming. This problem is heightened by an increase in the maximum number of modems which can be installed. Further, if modems are not frequently installed the cyclic or intermittent checking is wasteful.